Zinc-copper couple preparation

B. Cydopropylbenzene. In a 1-1. three-necked flask equipped, with a stirrer and a thermometer extending into the flask but free from the stirrer are placed 500 ml. of redistilled dimethyl-formamide and zinc-copper couple prepared from 131 g. (2 g. atoms) of zinc (Note 8). The mixture is cooled to 7° in an ice bath, and 1,3-dibromo-l-phenylpropane is added to the stirred mixture at a rate sufficient to maintain the reaction temperature at 7-9° (Note 9). The mixture is stirred for 30 minutes after the addition is completed, poured into 1 1. of water, and then steam-distilled until the condensate is homogeneous or 11. of water has been collected. The organic layer is separated from the distillate, and the aqueous layer is extracted with three 100-ml. portions of ether. The combined organic portions are washed with four 50-ml. portions of water and dried over anhydrous potassium carbonate. The ether is removed by distillation at atmospheric pressure at water bath temperature. The residue is distilled to give 88-100 g. (75-85%) of cydopropylbenzene, b.p. 170-175° (Note 10), 26d 1.5306-1.5318. 

The same group2 now finds that a zinc/copper couple prepared by sonication of Zn and Cul in ethanol/H20 (9 1) permits conjugate addition of alkyl halides to enones and enals. The order of reactivity is RI > RBr and tert > sec primary. THF/H20 or Py/HzO or even pure water can be used as solvent. This reaction can hardly involve a classical organometallic reagent, but probably involves an alkyl radical. 

Preparation of diethybinc. Zinc-copper couple prepared by either method 2 or 3 is placed in a dry flask equipped with a heavy stirrer and a reflux condenser and... 

Cleavage of 2,3-epoxy halidesA zinc-copper couple, prepared by sonication of zinc powder and Cui in aqueous ethanol, cleaves epoxy halides to a radical that rearranges to an allylic alcohol. Since the epoxy halide is prepared by epoxidation of an allylic alcohol (m-chloroperbenzoic acid) followed by reaction with P(ChH5)3 and CBr4, the reaction effects 1,3-transposition of the hydroxyl group. 

The Michael and related conjugate additions287 can be carried out in aqueous media. Alkyl groups add to electron-deficient alkenes using a zinc-copper couple prepared as described above. Sonication is necessary in practically all the examples published. The medium can consist of a mixture of water with lower alcohols, acetone, or even pyridine. In some cases, the composition corresponds to a maximum structuredness of the liquid, which parallels an optimal absorption of acoustic energy. ... 

Preparative Methods several methods for the preparation of bis[(trimethylsilyl)methyl]zinc have been reported. Addition of powdered anhydrous zinc(II) chloride to a solution of [(trimethylsilyl)methyl]magnesium chloride in diethyl ether at 0 °C and subsequent stirring for 4 days at room temperature affords the title compound in 90% yield after fractional distillation. A second route consists of the reaction of (iodomethyl)tri-methylsilane with zinc/copper couple (prepared by reduction of CuO with dihydrogen in the presence of zinc dust) at reflux for 3 h and affords the title compound in 56% yield. Bis[(trimethylsilyl)methyl]zinc can also be prepared quantitatively by reacting bis[(trimethylsilyl)methyl]mercury with an excess of zinc at ambient conditions. ... 

A mixture of 16a,17a-oxido-3a-acetoxy-16j( -methyl-5i( -pregnane-ll,12-dione, zinc-copper couple prepared from Zn-dust, and ethanol refluxed 2 days -> 3a-acetoxy-16-methyl-5/ -pregn-16-ene-ll,12-dione. Y 75%. F. e. s. S. M. Kupdian and M, Maruyama, J. Org. Chem. 36, 1187 (1971) with WCl6/n-C4HgLi s. K. B. Sharpless et al., Am. Soc. 94, 6538 (1972). 

An organozmc compound that occupies a special niche m organic synthesis is lodo methyhinc iodide (ICH2ZnI) It is prepared by the reaction of zinc-copper couple [Zn(Cu) zinc that has had its surface activated with a little copper] with diiodomethane m diethyl ether... 

In 1958 Simmons and Smith described a new and general synthesis of cyclopropanes by treatment of olefins with a reagent prepared from methylene iodide and a zinc-copper couple in ether solution. 

Monofluoroalkenes have been prepared by the addition of fluoromethylene-triphenylphosphorane generated m situ by treatment of fluoroiodomethyltri-phenylphosphomum iodide with zinc-copper couple in dimethylformamtde [49] (equation 47) (Table 181. 

The key step to this first reported case of the highly diastereoselective addition of a fluorinated enolate in an aldol process is the selective formation of the enolate a,a-Difluonnated enolates prepared by a metallation process employing either a zinc-copper couple [S] or reduced titanium species [9] undergo aldol condensation smoothly (equation 9) (Table 5)... 

The importance of solvent effects in the preparation of perfluoroalkyzinc reagents is further illustrated in the reaction of perfluoroalkyl iodides with zinc-copper couple. In DMSO, DMF, and HMPA, the main products are the fluo-roolefins The formation of the fluoroolefin is facilitated when the reaction is carried out in the presence of potassium thiocyanate [30] (equation 21)... 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

B) The preparation of (cis-1,2-epoxypropyi)phosphonic acid [ (1 -chloroethoxy )chloro-methyl] phosphonic acid (1.0 g) is added with stirring to tetrahydrofuran (50 ml) to which has been added a crystal of iodine and a zinc-copper couple (15.0 g). The mixture is then heated under reflux for 24 hr and the resulting solution filtered to yield (cis-1,2-epoxy propyl )-phosphonic acid. 

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... 

Buynak et al. reported the synthesis of representative 7-vinylidenecephalosporine derivatives bearing an axial allene chirality (Scheme 4.5) [9]. A chiral allene 24 was prepared stereoselectively utilizing the reaction of an organocopper reagent with propargyl triflate 23, obtained by a diastereoselective ethynylation of the ketone 22 with ethynylmagnesium bromide. Terminally unsubstituted allene 26 was synthesized via bromination of the triflate 23 followed by reduction of the bromide 25 with a zinc-copper couple. 

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

Solutions of low-valence titanium chloride (titanium dichloride) are prepared in situ by reduction of solutions of titanium trichloride in tetrahydrofuran or 1,2-dimethoxyethane with lithium aluminum hydride [204, 205], with lithium or potassium [206], with magnesium [207, 208] or with a zinc-copper couple [209,210]. Such solutions effect hydrogenolysis of halogens [208], deoxygenation of epoxides [204] and reduction of aldehydes and ketones to alkenes [205,... 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

An interesting reaction takes place when diketones with the keto groups in positions 1,4 or more remote are refluxed in dimethoxyethane with titanium dichloride prepared by reduction of titanium trichloride with a zinc-copper couple. By deoxygenation and intramolecular coupling, cycloalkenes with up to 22 members in the ring are obtained in yields of 50-95%. For example, 1-methyl-2-phenylcyclopentene was prepared in 70% yield from 1-phenyl-1,5-hexanedione, and 1,2-dimethylcyclohexadecene in 90% yield from 2,17-octa-decanedione [206, 210]. 

A modified procedure suitable for intramolecular reductive coupling is achieved using low-valence titanium prepared by reduction of titanium trichloride with a zinc-copper couple followed by the extremely slow addition of ketone to the refluxing reaction mixture (0.0003 mol over a 9-hour period by use of a motor-driven syringe pump) [S60. ... 

We have found that the method used to prepare the zinc-copper couple is an important variable in determining the efficiency and rate of these reactions. Optimal results are achieved using a couple prepared by brief 2 min) exposure of commercial zinc dust to twice the amount (0.06 equiv) of copper sulfate employed in the previous studies.We have also found that the cycloadditions proceed with equal efficiency and more conveniently by... 

A literature procedure for the preparation of the zinc-copper couple was followed except for the use of slightly more (28%) than the Indicated amount of copper sulfate. The checkers found that the kind of zinc used Is critical. Zinc dust, 325 mesh, from Aldrich Chemical Company, Inc. [catalog number 20,998-8] gave 7,7-d1chloro-l-methylb1cyclo[3.2.0]heptan-6-one in 80-89% yield. Zinc metal (dust) from Fisher Scientific Company (Lot 874394) gave the dichloro ketone In yields of 37-61% (five trials). The Fisher zinc was of unknown mesh, but was much more finely-divided than the Aldrich Chemical Company, Inc. zinc. 

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